Contact breaker points shielding means

ABSTRACT

An electrically insulated, resilient cylindrical sleeve gapped on one side to clip over adjacent ends of the contact breaker points of a magneto to enclose the working airgap and exclude fouling particles and matter therefrom. Peripheral enlargements adjacent the gap displacing the center of gravity towards the gapped portion of the sleeve to ensure that this portion remains beneath the points with changes in attitutde of the magneto to permit escape of stray particles and matter.

United States Patent Inventor William Henry Steele Mllperra, Australia Appl. No. 89,556 Filed Nov. 16, 1970 Patented Nov. 23, 1971 Assignee Victa Limited New South Wales, Australia Priority Nov. 17, 1969 Australia 63922/69 CONTACT BREAKER POINTS SHIELDING MEANS 9 Claims, 5 Drawing Figs.

US. Cl 220/168 H,

200/19 R, 200/166 L Int. Cl H01h 9/02 Field of Search 200/166 K,

166 L, 168 H, 1686, 19 R, 30

[56] References Cited UNITED STATES PATENTS 2,034,683 3/1936 Olandt 200/19 R X 2,619,555 11/1952 Westfall 200/168 G X 2,694,117 11/1954 Bakke..... 200/168HX 2,734,969 2/1956 Mallory 200/30 X Primary Examiner-H. 0. Jones Attorney-Waters, Roditi, Schwartz & Nissen ABSTRACT: An electrically insulated, resilient cylindrical sleeve gapped on one side to clip over adjacent ends of the contact breaker points of a magneto to enclose the working airgap and exclude fouling particles and matter lherefrmn. Peripheral enlargements adjacent the gap displacing the center of gravity towards the gapped portion of the sleeve to ensure that this portion remains beneath the points with changes in attitutde of the magneto to permit escape of stray particles and matter.

1 CONTACT BREAKER POINTS SHIELDING MEANS This invention relates to magneto design and more particularly to the shielding of the contact breaker points thereof.

The so-called conventional magnetos of the present day consist of a magnet and coil in relative motion, with the coil usually having primary and secondary windings. Usually a discrete phase relationship is maintained between the magnetic flux through the coil and the moment at which an open circuit is established in the primary winding of the coil.

Experience shows that the most unstable feature in this form of magneto is the resistance at the contact faces of the breaker points in the coil primary circuit. This is usually most influenced by environmental factors such as chemically reactive vapors, solids, or liquids: by mechanical deposition or sublimation of unwanted material: or by mechanical interposition between the points of granular material, such as silicaceous dust, pulverized earth etc.

The object of the present invention is to reduce the occurrence of unwanted material at the contact faces by shielding the points without affecting other features of the magneto function, and doing so in a way which is readily appreciated and understood by unfamiliar servicemen and which is cheap to manufacture.

The invention in one general form provides a shielding member for the contact breaker points of a magneto which include confronting studs of similar cross section anchored to relatively movable jaw mounts for repeated closing and opening within the limits of a maximum operating gap, said shielding member comprising a tubular electrically insulated body having an internal dimension closely and loosely to enclose the studs and having a length at least to span the maximum operating gap between the studs, at least one longitudinally extending lateral aperture in the bore of the tubular body, and a formation on a wall of the body offsetting the center of gravity of the body from its axis towards the lateral aperture, whereby said aperture automatically maintains a position beneath the contact breaker points with changed attitude of the magneto.

A preferred form of the invention is illustrated in the accompanying drawings in which:

FIG. 1 is a fragmentary perspective view of a typical engine with the flywheel removed to show the contact breaker points with a shield according to this invention in place thereon;

FIG. 2 is an enlarged perspective view of the breaker points also showing the shield in place;

FIG. 3 is a side elevation of the shield only;

FIG. 4 is a section on the line 4-4 in FIG. 3; and

FIG. 5 is a perspective view of a modified form of the invention.

In the preferred embodiment the shield 5 is formed of an electrically nonconductive material, preferably an acetal resin, such as that marketed under the name Delrin or Kematal," and comprises a cylindrical tubular body 6 with an internal bore 7 with chamfered side faces 8. A longitudinally extending radial gap 9 is preferably provided in the body 6 which is of resilient material of nonuniform thickness preferably by the provision of integral lobes 10 which extend from the periphery of the body on either side of the gap 9. The center of gravity of the shield 5 is displaced by the weight of the lobes 10, from the center of the bore 7, towards the gap 9.

The inner faces 11 of the body 6 that delineate the gap 9 are sprung apart as the shield 5 is snapped over the shanks of the fixed and moving contact breaker points 12 and 13, respectively, of an engine 14. The breaker points of magnetos usually comprise equal length confronting studs locked to an end portion of respective fixed and movable mounting arms or jaws 12A and 13A. Therefore, preferably the length of the shield 5 at least equals the combined length of either stud and the maximum opera ting gap therebetween but is less than the combined length of the studs to permit the points 12 and 13 to close, but enables the shield to cover the gap 15 between them at all times. The bore 7 will be of a diameter sufficient to enable the tubular body 6 to closely, yet loosely, enclose the breaker points 12 and 13 so that the body may rotate thereon yet exclude dust.

The weight of the lobes 10 causes the shields to maintain an attitude with the gap 9 at the underside of the contacts as shown in FIG. 2 even though the attitude of the engine 14 should change. The gap 9 also permits the free circulation of air to cool the bore 7 of said shield. The downward orientation of the gap 9 also ensures that any stray foreign particles that enter between the points 12 and 13 will fall freely therefrom and will not be trapped by the body 6 of the shield 5.

v The body 6 alternatively may be composed of a tube as shown in FIG. 5 having a thickened wall 16 on one side to displace the gravitational center of the body as explained above, and one or more rectangular, longitudinally extending lateral apertures such as grooves 17 in the region 16 of the wall surrounding the bore 7. The grooves 17 function in a similar manner for disposal of dust particles as the gap 9. This form of shield being shaped as a complete tube may only be fitted by separation of the magneto contact points to permit its insertion between the points.

It should be understood that other forms besides those described above are possible within the scope of this invention.

What I claim is:

l. A shielding member for contact breaker points of a magneto which include confronting studs of similar cross section anchored to relatively movable jaw mounts for repeated closing and opening within the limits of a maximum operating gap, said shielding member comprising a tubular electrically insulated body having an internal dimension closely and loosely to enclose the studs and having a length at least to span the maximum operating gap between the studs, at least one longitudinally extending lateral aperture in the bore of the tubular body, and a formation on a wall of the tubular body offsetting the center of gravity of the tubular body from its axis towards the lateral aperture, whereby said lateral aperture automatically maintains a position beneath the contact breaker points with changed attitude of the magneto.

2. A shielding member as claimed in claim 1, wherein the interruption in the tubular body is a radial gap permitting air circulation to the contact breaker points.

3. A shielding member as claimed in claim 2, wherein the tubular body is of nonuniform thickness so that the body's center of gravity is offset from the axis of the tubular body towards the radial gap, whereby said radial gap automatically maintains a position beneath the contact breaker points with changed attitude of the magneto.

4. A shielding member as claimed in claim 3, wherein the tubular body has integral peripheral lobes at opposite sides of the radial gap.

5. A shielding member as claimed in claim 4, wherein the confronting faces of the tubular body which border the radial gap are oppositely radiused.

6. A shielding member as claimed in claim 1, wherein the width of the tubular body at least equals the combined length of said maximum operating gap and any one of said studs and is less than the combined length of said studs, whereby said tubular body at all times spans the operating gap and does not prevent closing of said studs.

7. A shielding member as claimed in claim 1, wherein the side edges of the tubular body are chamfered.

8. Ashielding member for enclosing the operating gap between contact breaker points of a magneto which are composed of two similar, axially aligned, cylindrical studs extending from relatively movable mounting jaw arms for closing together and opening confronting ends of the studs within the limits of a maximum operating airgap between the studs, said shielding member comprising a radially gapped hollow cylindrical body composed of electrically insulating and resilient thermoplastic material and whose internal diameter is slightly greater than the external diameter of the studs and whose length exceeds the combined extending length of a stud and the length of the maximum operating airgap and is less than the combined extending length of both studs, and integral protuberances on the periphery of the body adjacent opposite sides of the radial gap to locate the body's center of gravity to one side of the body's axis towards the radial gap. 9. A shielding member as claimed in claim 8, wherein the 5 body is composed of an acetal resin. 

1. A shielding member for contact breaker points of a magneto which include confronting studs of similar cross section anchored to relatively movable jaw mounts for repeated closing and opening within the limits of a maximum operating gap, said shielding member comprising a tubular electrically insulated body having an internal dimension closely and loosely to enclose the studs and having a length at least to span the maximum operating gap between the studs, at least one longitudinally extending lateral aperture in the bore of the tubular body, and a formation on a wall of the tubular body offsetting the center of gravity of the tubular body from its axis towards the lateral aperture, whereby said lateral aperture automatically maintains a position beneath the contact breaker points with changed attitude of the magneto.
 2. A shielding member as claimed in claim 1, wherein the interruption in the tubular body is a radial gap permitting air circulation to the contact breaker points.
 3. A shielding member as claimed in claim 2, wherein the tubular body is of nonuniform thickness so that the body''s center of gravity is offset from the axis of the tubular body towards the radial gap, whereby said radial gap automatically maintains a position beneath the contact breaker points with changed attitude of the magneto.
 4. A shielding member as claimed in claim 3, wherein the tubular body has integral peripheral lobes at opposite sides of the radial gap.
 5. A shielding member as claimed in claim 4, whErein the confronting faces of the tubular body which border the radial gap are oppositely radiused.
 6. A shielding member as claimed in claim 1, wherein the width of the tubular body at least equals the combined length of said maximum operating gap and any one of said studs and is less than the combined length of said studs, whereby said tubular body at all times spans the operating gap and does not prevent closing of said studs.
 7. A shielding member as claimed in claim 1, wherein the side edges of the tubular body are chamfered.
 8. A shielding member for enclosing the operating gap between contact breaker points of a magneto which are composed of two similar, axially aligned, cylindrical studs extending from relatively movable mounting jaw arms for closing together and opening confronting ends of the studs within the limits of a maximum operating airgap between the studs, said shielding member comprising a radially gapped hollow cylindrical body composed of electrically insulating and resilient thermoplastic material and whose internal diameter is slightly greater than the external diameter of the studs and whose length exceeds the combined extending length of a stud and the length of the maximum operating airgap and is less than the combined extending length of both studs, and integral protuberances on the periphery of the body adjacent opposite sides of the radial gap to locate the body''s center of gravity to one side of the body''s axis towards the radial gap.
 9. A shielding member as claimed in claim 8, wherein the body is composed of an acetal resin. 